An insulated-gated field-effect transistor (IGFET), such as a metal-oxide semiconductor field-effect transistor (MOSFET), uses a gate to control an underlying surface channel joining a source and a drain. The channel, source and drain are located within a semiconductor substrate, with the source and drain being doped oppositely to the substrate. The gate is separated from the semiconductor substrate by a thin insulating layer such as a gate oxide. The operation of the IGFET involves application of an input voltage to the gate, which sets up a transverse electric field in the channel in order to modulate the longitudinal conductance of the channel.
The functioning of IGFETs can be altered by various contaminants. Primary among them are chemicals such as sodium and chlorine. Additionally, other chemicals can attack the layers of IGFETs, and environmental factors, such as particulates, humidity, and static can ruin IGFETs or change their performance. Other concerns are the influence of light and radiation impinging on the surface of an IGFET. Some IGFETs may be extremely light or radiation sensitive. This factor is considered in the selection of packaging materials and processing of the IGFETs. A dominant IGFET characteristic is the extreme vulnerability of its surface to physical abuse. The surface components of a particular integrated circuit containing many IGFETS, for example, are only a small distance down into the wafer surface.
These environmental and physical concerns are typically addressed via the deposition of a passivation layer near the end of the fabrication process. This layer is known by several different names, such as silox, vapox, pyrox, glassivation layer, PSG, BSG, and PBSG. Two materials commonly used for the passivation layer are silicon dioxide and silicon nitride. Thus, the passivation layer is a sealing layer added at the end of the fabrication process to prevent or retard deterioration of electronic properties through chemical action, corrosion, or handling during the packaging processes, and thus protects against moisture and contamination.
Passivation layers such as silicon dioxide and silicon nitride, however, do not prevent all such deterioration, nor do they completely protect against all moisture and contamination. There is a need, therefore, for better, more preventative and more protective passivation layers.